Hazards Notes 8th Social Science

Hazards Notes 8th Social Science

8th Social Science Lesson 14 Notes in English

14. Hazards

  • In the beginning of twenty-first century, the earth supported a human population that was more numerous and found healthier and wealthier than ever before.
  • At the same time, there were a lack of awareness on the risks that faced by the people.
  • By keeping this in mind, the present lesson of hazards is intended to familiarise the different types of hazards to promote awareness among students regarding hazards.
  • Hazards are defined as a thing, person, event or factor that poses a threat to people, structures or economic assets and which may cause a disaster.
  • They could be either human made or naturally occurring in the environment.
  • The word ‘hazard’ owes its origin to the word ‘hasart’ in old French meaning a game of dice (in Arabic – az-zahr; in Spanish – azar).
  • Though the society experiences several types of hazards, it is important for a region to be aware of those threats that are most likely to affect the community most severely.

Types of Hazards

Some hazards occur frequently and threat the people. Hazards are classified in different ways.

  • Based on their causes of occurrence.
  • Based on their origin.

Based on their causes of occurrence

Hazards can be broadly classified into three types: natural, human-made and socio-natural hazards.

Natural hazards:

  • These are the results of natural processes and man has no role to play in such hazards.
  • The main examples of natural hazards are earthquakes, floods, cyclonic storms, droughts, landslides, tsunamis and volcanic eruptions.

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Human-made hazards:

  • These are caused by undesirable activities of human. It can be the result of an accident, such as an industrial chemical leak or oil spill, or an intentional act.
  • Such hazards can disturb the safety, health, welfare of people and cause damage or destruction to property.
  • The following are the examples of human-made hazards.
  • They are explosions, hazardous wastes, pollution of air, water and land, dam failures, wars or civil conflicts and terrorism.

Socio-natural hazards (Quasi-natural hazards)

  • These are caused by the combined effect of natural forces and misdeeds of human. Some of the examples are
  • The frequency and intensity of floods and droughts may increase due to indiscriminate felling of trees, particularly in the catchment areas of the rivers.
  • Landslides are caused by natural forces and their frequency, and impact may be aggravated as a result of construction of roads, houses etc., in mountainous areas, excavating tunnels and by mining and quarrying.
  • Storm surge hazards may be worsened by the destruction of mangroves.
  • Smog is a serious problem in most big urban areas.
  • The emissions from vehicles and industries, combustion of wood and coal together combined with fog leads to smog.

Based on their origin

Hazards can be grouped into eight caregories

Atmospheric hazard – Tropical storms, Thunderstorms, Lightning, Tornadoes, Avalanches, Heat waves, Fog and Forest fire.

Geologic/Seismic hazard – Earthquakes, Tsunamis, Landslides and Land subsidence.

Hydrologic hazard – Floods, Droughts, Coastal erosion and Storm surges.

Volcanic hazard – Eruptions and Lava flows.

Environmental hazard – Pollution of soil/ air/water, Desertification, Global warming and Deforestation.

Biological hazard – Chickenpox, Smallpox, AIDS [HIV] and Killer bees.

Technological hazard – Hazardous material incidents, Fires, Infrastructure failures [Bridges, Tunnels, Dams] and Nuclear/ Radiological accidents.

Human-induced hazard – Terrorism, Mass shootings, War, Transportation accidents and Civil disorder.

Major Hazards in India:



  • Earthquake is a violent tremor in the earth’s crust, sending out a series of shock waves in all directions from its place of origin.
  • Earthquake prone regions of the country have been identified on the basis of scientific inputs relating to seismicity, earthquakes occurred in the past and tectonic setup of the region.
  • Based on these inputs, Bureau of Indian Standards has grouped the country into four seismic zones: Zone II, Zone III, Zone IV and Zone V (No area of India is classified as Zone I).

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Flood is an event in which a part of the earth’s surface gets inundated. Heavy rainfall and large waves in seas are the common causes of flood.

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The major causes of floods are:

Meteorological factors

  • Heavy rainfall
  • Tropical cyclones
  • Cloud burst

Physical factors

  • Large catchment area
  • Inadequate drainage arrangement

Human factors

  • Deforestation
  • Siltation
  • Faulty agricultural practices
  • Faulty irrigation practices
  • Collapse of dams
  • Accelerated urbanisation

Gangetic plains covering the states of Punjab, Haryana, Uttar Pradesh, North Bihar, West Bengal and Brahmaputra valley are the major flood prone areas in north and northeast India. Coastal Andhra Pradesh, Odisha and southern Gujarat are the other regions which are also prone to flood often.

Cyclonic Storms

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  • A cyclonic storm is a strong wind circulating around a low pressure area in the atmosphere.
  • It rotates in anti-clockwise direction in Northern Hemisphere and clockwise in the Southern Hemisphere.
  • Tropical cyclones are characterised by destructive winds, storm surges and exceptional levels of rainfall, which may cause flooding.
  • Wind speed may reach upto 200 km/h and rainfall may record upto 50 cm/day for several consecutive days.
  • A sudden rise of seawater due to tropical cyclone is called storm surge. It is more common in the regions of shallow coastal water.

East coastal areas vulnerable to storm surges

North Odisha and West Bengal coasts.

Andhra Pradesh coast between Ongole and Machilipatnam.

Tamil Nadu coast (among 13 coastal districts, Nagapattinam and Cuddalore districts are frequently affected).

West coastal areas vulnerable to storm surges

The west coast of India is less vulnerable to storm surges than the east coast.

Maharashtra coast, north of Harnai and adjoining south Gujarat coast and the coastal belt around the Gulf of Cambay.

The coastal belt around the Gulf of Kutch.


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Any lack of water to satisfy the normal needs of agriculture, livestock, industry or human population may be termed as a drought. Further, the drought could be classified into three major types as,

Meteorological drought: it is a situation where there is a reduction in rainfall for a specific period below a specific level.

Hydrological drought: it is associated with reduction of water in streams, rivers and reservoirs. It is of two types

  • Surface water drought
  • Groundwater drought.

Agricultural drought: it refers to the condition in which the agricultural crops get affected due to lack of rainfall.

  • Droughts in India occur in the event of a failure of monsoon. Generally monsoon rainfall is uneven in India.
  • Some areas receive heavy rainfall while other regions get moderate to low rainfall.
  • The areas which experience low to very low rainfall are affected by drought.

The major areas highly prone to drought are:

  • The arid and semi-arid region from Ahmedabad to Kanpur on one side and from Kanpur to Jalandhar on the other.
  • The dry region lying in the leeward side of the Western Ghats.


  • Landslide is a rapid downward movement of rock, soil and vegetation down the slope under the influence of gravity.
  • Landslides are generally sudden and infrequent. Presence of steep slope and heavy rainfall are the major causes of landslides.
  • Weak ground structure, deforestation, earthquakes, volcanic eruptions, mining, construction of roads and railways over the mountains are the other causes of landslides.
  • About 15% of India’s landmass is prone to landslide hazard. Landslides are very common along the steep slopes of the Himalayas, the Western Ghats and along the river valleys.
  • In Tamil Nadu, Kodaikanal (Dindigul district) and Ooty (The Nilgiris district) are frequently affected by landslides.


  • Tsunami refers to huge ocean waves caused by an earthquake, landslide or volcanic eruption.
  • It is generally noticed in the coastal regions and travel between 640 and 960 km/h.
  • Tsunamis pose serious danger to the inhabitants of the coastal areas.

Hazardous Wastes

  • The wastes that may or tend to cause adverse health effects on the ecosystem and human beings are called hazardous wastes.

The following are the major hazardous wastes

Radioactive substance: tools and unused fuel rods of nuclear power plants.

Chemicals: synthetic organics, inorganic metals, salts, acids and bases, and flammables and explosives.

Biomedical wastes: hypodermic needles, bandages and outdated drugs.

Flammable wastes: organic solvents, oils, plasticisers and organic sludges.

Explosives: the wastes resulting from ordnance manufacturing and some industrial gases.

Household hazardous wastes: pesticides, waste oil, automobile battery and household battery.

Pollution of Air

  • Air is a mixture of several gases. The main gases are nitrogen (78.09%) for forming products such as, fertilisers for plants and for making the air inert, oxygen (20.95%) for breathing and carbon dioxide (0.03%) for photosynthesis.
  • Some other gases like argon, neon, helium, krypton, hydrogen, ozone, zenon and methane are also present.
  • Besides, water vapour and dust particles make their presence felt in one way or the other.
  • Air pollution is the contamination of the indoor or outdoor air by a range of gases and solids that modify its natural characteristics and percentage.
  • Air pollutants can be categorised into primary and secondary pollutants. A primary pollutant is an air pollutant emitted directly from a source.
  • A secondary pollutant  is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

Primary Pollutants

  • Oxides of sulphur
  • Oxides of Nitrogen
  • Oxides of Carbon
  • Particulate Matter
  • Other Primary Pollutants

Secondary Pollutants

  • Ground Level Ozone
  • Smog

Pollution of Water

  • Water pollution may be defined as alteration in the physical, chemical and biological characteristics of water, which may cause harmful effects in human and aquatic life.
  • In India, water pollution has been taking place on a large scale and since a long period.
  • Both surface and groundwater bodies are polluted to a great extent.

The major causes of water pollution in India are:

  • Urbanisation
  • Industrial effluents
  • Sewages
  • Agricultural runoff and improper agricultural practices
  • Seawater intrusion
  • Solid wastes

Need for Prevention Measures

Prevention is defined as the activities taken to prevent a natural calamity or potential hazard from having harmful effects on either people or economic assets.

Prevention planning consists of,

  • Hazard identification
  • vulnerability assessment.

Delayed actions may increase the economic losses.

For developing countries like India, prevention is perhaps the most critical components in managing disasters.

More to Know:

1. A natural hazard is a natural process and event that is a potential threat to human life and property. The process and events themselves are not a hazard but become so because of human use of the land. A disaster is a hazardous event that occurs over a limited time span in a defined area and causes great damage to property/ loss of life, also needs assistance from others. A catastrophe is a massive disaster that requires significant expenditure of money and a long time (often years) for recovery.

2. About one third area of the country is affected by drought. It severely affects 16% of the land area and 12% of the total population of India. The areas that receive an annual rainfall of less than 60 cm are the drought prone regions of India.

3. The word ‘Tsunami’ is derived from Japanese word ‘tsu’ meaning harbour and ‘nami’ meaning wave (Harbour wave).

4. Indian Ocean Tsunami of 2004

  • On December 26, 2004, at 7:59 a.m. local time, an undersea earthquake with a magnitude of 9.1 struck off the coast of the Indonesian island of Sumatra.
  • The tsunami killed at least 2,25,000 people across a dozen countries, with Indonesia, Sri Lanka, India, Thailand, Somalia and Maldives, sustaining massive damage.

5. Chernobyl nuclear disaster site (near Pripyat) to become an official tourist spot


  • Chernobyl (then Soviet Union) nuclear accident was happened on 26th April, 1986.
  • The radiation emitted was more than 400 times than that released by the atomic bomb dropped on Hiroshima (Japan) in 1945.
  • This accident remains the largest nuclear accident in history.
  • More than 3,50,000 people were evacuated from the area and severe restrictions on permanent human settlement are still in that place.


  • 33 years after the accident, the Exclusion Zone, which covers an area now in Ukraine and Belarus is inhabited by numerous animals and more than 200 bird species.
  • In 2016, the Ukraine part of this zone was declared as a radiological and environmental biosphere reserve by the government.

6. Nature is emerging as a new weapon of mass destruction, do you agree?

Around 22,000 people have died in India in 10 years until 2017 due to major environmental disasters – Indian Meteorology Department. In the past two decades (1998-2017) over 5,00,000 people have died due to extreme weather events around the world – stated by Global Climate Risk Index Report Published by Germanwatch (German-based non-profit organisation).

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